1. Field of the Invention
The present invention relates to an image forming system that forms a color toner image and a transparent toner image on a recording material, a controlling apparatus that controls the image forming system, and a recording medium that has a program recorded therein.
2. Description of the Related Art
In recent years, in order to increase a gloss of an image, image forming apparatuses using a transparent toner have been suggested. For example, Japanese Patent Application Laid-Open No. 2006-243209 discloses an image forming apparatus where a transparent toner image is formed to overlap a color toner image on a recording material, thereby forming an image having a high gloss. A fixer of the image forming apparatus includes a pair of fixing rollers that include heaters. In a heating nip portion that is formed by the pair of fixing rollers, a toner image on the recording material is fixed to the recording material. This fixing system is called a high temperature separation system.
Further, Japanese Patent Application Laid-Open No. 2002-341619 discloses an image forming apparatus where a transparent toner image is formed to overlap a color toner image on a recording material, thereby forming an image having a high gloss. A fixer of the image forming apparatus heats a toner image on the recording material with a fixing belt having a smooth surface, and separates the cooled recording material from the fixing belt in a state where the recording material closely adheres to the fixing belt. This fixer is called a fixer of a cooling separation system. In the fixer of the cooling separation system, the toner image is solidified in a state where the toner image closely adheres to a surface of the fixing belt. As a result, a surface of the toner image is smoothened like the surface of the fixing belt.
In this case, in order to adjust a gloss of a printed material, an image forming system that has a fixer of a high temperature separation system and a fixer of a cooling separation system is assumed. In this image forming system, in order to adjust a gloss of an image, a mode where an image is fixed using the fixer of the high temperature separation system and a mode where an image is fixed using the fixer of the cooling separation system are considered. When the gloss of the image is increased using the fixer of the high temperature separation system, a transparent toner of the predetermined amount per unit area is loaded to the recording material. In the same way, when the gloss of the image is increased using the fixer of the cooling separation system, if a transparent toner of the same amount per unit area as that in the case where the gloss of the image is increased using the fixer of the high temperature separation system is loaded, a crack may be easily generated in the surface of the image.
The reason why the crack is generated is as follows. If the recording material is heated, moisture is evaporated and the recording material is contracted. Further, if the recording material is cooled down after being heated, the recording material absorbs moisture and is expanded. Meanwhile, if a toner is heated, the toner is expanded while being softened. Further, if the toner is cooled down, the toner is contracted while being solidified. For this reason, in the high temperature separation system, since the toner whose viscosity is lowered is gradually solidified along the expanded recording material, it is difficult for a crack to be generated in the toner image. Meanwhile, in the cooling separation system, since the toner is rapidly cooled down, the toner is solidified in a state where strong stress remains in the toner. Thereafter, due to the expansion of the recording material, the crack may be easily generated in the toner image.